top of page

Reference CTP-SAI-076

Exploring the mechanism underpinning determinacy and nitrogen requirement in potato crops

Reference CTP-SAI-076

Exploring the mechanism underpinning determinacy and nitrogen requirement in potato crops

Dr Johannes Kromdijk (University of Cambridge),
Dr Stéphanie Swarbreck (NIAB),
Dr Sarah Roberts (NIAB),
David Almond (CUPGRA)


Potato is the most important non-grain crop worldwide. It is a high yielding and high value crop with gross margins for the top 25 % of UK crops c.£9,000/ha (compared to £1,200/ha for winter wheat, 2017-2020 AHDB). However, conventional agricultural practice relies on large applications of nitrogen (N)-based mineral fertilizers to achieve these high potato yields. To ensure that N does not limit crop growth, applications are often in excess of crop needs resulting in environmental issues as excess N may leach from fields and pollute local waterways resulting in eutrophication and production of nitrous oxide a potent greenhouse gas. Excess N applications are a waste of resources including the energy and raw materials required to make the fertilizer, and of farm finances when continued N application does not deliver increased yields or improved profit margins. In addition, these can have a negative impact on potato yield quality, reducing starch and dry matter content as well as reducing yield tonnage.

In potato N recommendations are heavily informed by varietal determinacy—the propensity of a plant to continue leaf production after flowering. Varietal determinacy underpins differences in growth habits; determinate varieties produce more compact canopies due to leaf production restricted to early growth (ceasing leaf production after flowering in the most determinate varieties), whilst leaf production continues throughout the growing season in indeterminate varieties resulting in large, sprawling canopies. Whilst potato architecture is also influenced by environmental conditions, agronomy and seed physiology, the variety’s ability to respond to those conditions is set by determinacy. Determinate varieties can require twice as much nitrogen as indeterminate varieties to maintain growth for the same length of season. However, little is known about the processes which link determinacy and nitrogen requirement.

Hence it is important to understand what drives differences in nitrogen partitioning within potato plants and how varieties of different determinacy respond to N applications—key components of nitrogen use efficiency (NUE)—to be able to reduce the practice of over-fertilisation.



This project aims to gain insights into the mechanism of potato plants response to N application, and the increased N requirement for determinate compared to indeterminate varieties, and will do so by addressing these three questions:

1) How do determinate and indeterminate potato crops contrast in N uptake and partitioning throughout development? This will involve quantifying biomass partitioning, above- and below-ground plant architecture, and sap analysis across a range of N rates in the first half of the season through sequential harvests, as well as N uptake measurements.

2) Are the N uptake and assimilation processes differentially regulated at the molecular levels in determinate and indeterminate varieties, and in response to varied N supply? This will involve monitoring the transcript abundance of key genes involved in N metabolism and linking to carbon assimilation and leaf level photosynthesis, and the whole plant responses.

3) How N rate can affect the timing of tuberization and ultimately yield production, with respect to determinacy? The student will test whether different N management regimes (varying timings and products) can reduce N application without compromising yield.


This project will improve our mechanistic understanding of the variation in N uptake between varieties to enable precision application of N—reducing waste of raw materials, energy and farm financial resources, reducing N run-off and eutrophication and improving tuber quality. It will also provide a framework through which to understand the effects of alternative sources on N and application strategies in potato.


The student will be registered with the University of Cambridge and based at NIAB, Cambridge.


Students will have unlimited access to training courses provided by the University of Cambridge, alongside access to training in key bioscience areas (bioinformatics, statistics and mathematics) to enhance employability and research capability. The student will also have regular opportunities to present findings to interested potato growers and industry members throughout their project at the CUPGRA Members’ Days and annual Research Review meetings.

The CTP – SAI ( is a groundbreaking partnership between leading businesses, charities and research providers offering outstanding training for the agri-food sector.  All CTP-SAI students will receive the Leadership and Management training provided by MDS ( and will create their Personal Development Plan (PDP) to identify their development needs and areas of strength. Each student will receive individual coaching and mentoring with regards to their career plans and skills development (in addition to the scientific project supervision).


Placements are a key feature of CTP and UKRI-BBSRC expects all doctoral candidates on a CTP programme to undertake a placement. Placements can be in the form of research placements (3-18 months duration) or used more flexibly for experiential learning of professional skills for business and/or entrepreneurship. All placements are developed in collaboration between the partners with input from the doctoral candidate.


Contact Stéphanie Swarbreck ( and Sarah Roberts ( for an informal discussion on the research content of this PhD.

This studentship will begin in October 2024. The successful candidate should have (or expect to have) an Honours Degree (or equivalent) with a minimum of 2.1 in Plant Science, Applied Statistics, or other related science subjects. Students with an appropriate Masters degree are particularly encouraged to apply.

This studentship is for four years and is fully funded in line with UKRI-BBSRC standard rates. These will be for 2024/2025, an annual maintenance stipend of £19,237, fee support of £4,786, a research training support grant of £5,000 and conference and UK fieldwork expenses of £300.

Due to funder-mandated caps for the CTP as a whole, this project is only available to ‘Home’ applicants

To be classed as a home student, candidates must meet the following criteria:

  • Be a UK National (meeting residency requirements), or

  • Have settled status, or

  • Have pre-settled status (meeting residency requirements), or

  • Have indefinite leave to remain or enter

If a candidate does not meet the criteria above, they would be classed as an international student would not be eligible for this round of recruitment.

Anyone interested should complete the online application form before the deadline of 17th June 2024. Interviews will be held during June 2024.

Please contact for further application details.

NIAB logo transparent background_edited.jpg
NIAB logo transparent background_edited.jpg
NIAB logo transparent background_edited.jpg
  • LinkedIn
  • Twitter
  • Instagram
bottom of page